A giant magnetoresistance (GMR) element including a multilayer film having a ferromagnetic layer and a nonmagnetic layer, and a tunneling magnetoresistance (TMR) element in which an insulating layer (a tunnel barrier layer, and a barrier layer) is used as a nonmagnetic layer are known. In general, a TMR element has a higher element resistance than a GMR element, and its magnetoresistance (MR) ratio is larger than that of a GMR element. Therefore, attention is being paid to TMR elements, as elements for magnetic sensors, high-frequency components, magnetic heads and nonvolatile random access memories (MRAM).
An MRAM reads and writes data by utilizing characteristics in which the element resistance of the TMR element varies when the directions of magnetization of the two ferromagnetic layers sandwiching the insulating layer change. As a writing method of an MRAM, there is a method of writing (magnetization reversal) using a magnetic field generated by a current, or a method of writing (magnetization reversal) using a spin transfer torque (STT) generated by causing a current to flow in a stacking direction of the magnetoresistance effect element. Although the magnetization reversal of the TMR element using an STT is efficient from the viewpoint of energy efficiency, the reversal current density for magnetization reversal is high. In order to improve the durability of a TMR element, it is preferable that the reversal current density be low. This also applies to a GMR element.
In recent years, attention has focused on magnetization reversal which utilizes a pure spin current generated by a spin orbit interaction (for example, Non-Patent Document 1), as method for reducing the reversal current provided by a mechanism different from an STT. A pure spin current caused by a spin orbit interaction or the Rashba effect at an interface of dissimilar materials induces a spin orbital torque (SOT) and causes magnetization reversal using an SOT. Also, even with a pure spin current caused by the Rashba effect at an interface of dissimilar materials, a similar magnetization reversal due to an SOT occurs. However, these mechanisms have not yet been clarified. Pure spin current is created by the same number of electrons of upward spin and electrons of downward spin flowing in mutually opposite directions, and the flows of electric charge cancel each other out. Therefore, the current flowing through the magnetoresistance effect element is zero and does not damage the magnetoresistance effect element.
However, it has been reported in Non-Patent Document 1 that the reversal current density due to an SOT in the current element structure is about the same as the reversal current density due to an STT. Although a current flow that produces a pure spin current does not damage a magnetoresistance effect element, reduction of the reversal current density is required from the viewpoint of driving efficiency. In order to reduce the reversal current density, it is necessary to generate a pure spin current more efficiently. Non-Patent Document 2 discloses that the generation efficiency of a pure spin current increases as the resistivity of the spin orbit torque wiring which is a member for generation increases. If the generation efficiency of pure spin current increases, the current density (reversal current density) for reversing the magnetization can be kept low, and in order to realize this, there is a requirement for a technique for increasing the resistivity of the spin orbit torque wiring.